It depends on what you are asking for... If you are on android, download ChromeCast app from the GooglePlay Store. I don't use other app stores. If you are wanting to tabcast from Chrome browser, download the extension.
Otherwise, you will look for the chromecast icon (a screen with a couple of lines in the upper right corner) to cast it onto your television. It will only show up if you have the television turned on to that station, and the network has detected that the chromecast dongle is on!